A five-and-a-half-hour marathon of 52 contemporary plays, “The Mysteries” tells the story of the Old and New Testaments and features 48 members of the Bats, the Flea’s resident company. Following a successful eight-week run in the spring, most of the cast returned for a monthlong extension. By the time the show closes, on July 14, they will have invested eight months of their lives, arranging paying jobs — and searches for paying jobs — around it.Alice Allemano, who plays Gabriel, laughingly likened the company to a kibbutz: The lack of pay creates an unusual atmosphere of equality among the actors.

“Everybody is a really important cog of the machine,” she explained. “Backstage, we all do everything. We do the washing up; we do each other’s hair and makeup.”

In an age when unpaid internships and other work for free have become litigious, the Flea’s way of doing things has drawn heat, particularly after it announced plans in December to build an $18.5 million home not far from its rented space on White Street, where a full-time staff of eight toils in a glamour-free subbasement. (The theater’s annual budget is $1.3 million.)